Magnetic material detector



Jan. 14, 1941. H. E. wURzBAcH MAGNETIC MATERIAL DETECTOR 2 Sheets-Sheet 1 VVV (N060 c on A i A (28a @u QQ Filed March 14, 19258 v v V Af( l ATTORNEYS.

Jan. 14, 1941. H. E. wURzBAcH MAGNETIC MATERIAL DETECTOR Filed March 14, 1938 2 Sheets-Sheet 2 xNvENToR ffy/5E Wfl/1fach BY m @4% fw f ATTORNEYS,

Patented Jan. 14, 1941 UNITED STATES "PATENT ori-'ica 2Claims.

This invention is concerned with an apparatus for detecting the presence of a moving body of magnetic material and pertains more particularly to an apparatus for the detection of a magnetic contaminant present in a mass of nonmagnetic material while said mass of material is in motion, as for example, for the. detection of a magnetic substance in a body of material on a moving conveyor belt, or on the person of an individual passing through a doorway or the like.

The principal object of the invention is to provide an apparatus for detecting the presence of a body of magnetic material such as small iron, steel, or nickel masses when they are present among non-magnetic materials which are being conveyed from one point to another or are ,being changed from one container to another.

In milling operations in which crushingmchinery is used to pulverize the ore in the process of mill concentrate treatment it is not unusual for mine drills or parts thereof or parts of mining machinery to be present ln the ore. If these parts are allowed to enter the crushing machinery with the ore they may cause considerabie damage thereto, especially if they are of iron or steel. In large operations the ore is fed to the crusher or the like on conveyor belts which may be of considerable width, and it is a particular object of `this invention to provide an apparatus for detecting the presence of a harmful foreign body in the relatively large body of ore moving on such conveyor belt, such detection being based on the magnetic properties of such foreign body and being effected by subjecting such a body of material to magnetic scrutiny.

A further object of the invention is to associate a suitable work circuit with the detecting apparatus so that certain operations will be performed upon the detection of a given sized moving body of magnetic material.

The apparatus may comprise a magnetic circuit which includes an air path of substantial dimensions interposed in the path of the body of magnetic material, and means are included in the magnetic circuit for producing a substantially constant magnetic flux therein. A detector coil is positioned so as in be linked by at least a portion of the flux in the magnetic circuit, and a work circuit is associated with the detector coil and is responsive to changes in voltage induced in the detector coil by changes of flux in the magnetic circuit. These changes in flux are produced by the changes in reluctance of the magnetic circuit brought about by the movement of a magnetic body through the air path.

In some embodiments oi my invention, particularly in the smaller 'embodiments thereof. s the magnetic flux may be produced by permanent magnets. In all embodiments of my invention, I prefer to form the maior portion of the magnetic circuit as an iron core which provides two or more pole members, and the air path portion of the magnetic circuit will comprise the air paths between the various pole members. The work circuit may comprise suitable means for causing the operation of a signal to indicate the presence of a body of magnetic l material, or means for causing the stoppe of the machinery such as the conveyor belt or crusher, and if desired, means for recording and indicating the frequency at which magnetic material has passed a given point. The work cir- 4cuit may also comprise means for removing the body of magnetic material, either directly or along with other material. Further objects and advantages of the invention will either to specically brought out in the following description or will bey apparent therefrom. I have illustrated apparatus according to my invention in the accompanying drawings, and referring thereto:

Fig. 1 is a diagrammatic representation of a simple form of apparatus according to my invention;

Fig. 2 `is a diagrammatic representation of a modified form of apparatus;

Fig. 3 is a diagrammatic representation of a further modined form of apparatus;

Fig. 4 is a partly sectional front elevation of a form of apparatus comparable to that shown in Fig. 2;

Fig. 5 is an end elevation thereof;

Fig. 6 is a sectional view thereof taken on line 6-6 in Fig. 4; and

Figs. 7 and 9 illustrate circuit arrangements useful' according to the present invention, while Fig. 8 illustrates an application of the detector to a passageway or the like.

Referring to Fig. 1, a simple form of apparatus is shown as comprising a c-shaped core l of magnetic material such as transformer laminations providing a pair of opposing pole members 2 and l disposed on laterally opposite sides of a conveyor belt l upon which is a body of material 5. The magnetic circuit comprises the core I and the air path between the poles I and 6l l, which alr path is interposed in the path o! material on the conveyor belt l. The conveyor belt may be assumed to be moving either toward or away from the planeo! the paper and the air path between the poles 2 and 8 may be considered as transverse to the conveyor belt and to the path of movement oi the material carried thereon. The core I Afurther comprises a winding 8 having terminals I and 8 which are adapted for connection to a suitable constant voltage source of direct current and which is adapted to energize the core I and the magnetic circuit to produce a substantially constant nux therein. The apparatus further comprises a pair of detector coils 8 and I0 mounted on the core I, as at the pole members 2 and 8 and adapted to be linked by at least a portion oi' the flux in the magnetic circuit. The detector coils are shown connected in series and to a pair of terminals II and I2 which may be associated with a suitable work circuit.

Assuming now that the terminals I and 8 have been connected to a suitable direct current source and that a substantially constant iiux is present in the magnetic circuit, there will be no appreciable voltage generated in the coils 8 and III and consequently no voltage across the terminals II and I2. As long as the material 5 on the conveyor belt 4 is practically non-magnetic in character, there will be no change in the magnetic circuit as the material passes through the air path between the pole members 2 and 3; however, if a small body oi magnetic material is present in the material 5 it will, upon approaching the air path between the poles 2 and 3, decrease the reluctance of this air path and cause an abrupt change in the amount oi ilux linking the detector coils 9 and I0. This change in reluctance and the consequent change in nux will cause a voltage to be induced in either one or both of the coils 9 or I0 and a potential difierence will be created between the terminals II and I2, which potential diiierence may be used to cause a work circuit connected to the terminals II and I2 to perform certain operations.

With the arrangement shown, the approximate center of the body of material carried on the conveyor belt 4 should lie approximately centrally between the two pole members 2 and 3, so that the eilect produced by a body of magnetic material of a given size will be practically the same, irrespective of its position in the body of material 5. It should be mentioned that the relative dimensions of the parts of the core I depend largely upon the position of the belt 4 with respect to the core and upon the width and thickness of the material carried by the belt. These dimensions will thus be modified to meet various conditions, as will be apparent to those skilled in the art. In general, the spacing of the poles 2 and 3 will be less than the distance between one face and the back leg Ia of the core I at the opposite end of the coil 8. This condition will be adequately met if the distance A between the psies and lthe back leg la is not allowed to be less than the inter-pole spacing.

t may also be mentioned that numerous forms of connection may be made for the detector coils 9 and I0. For example, they may be connected either in series, or in parallel in additive or subtractive relation, depending upon the particular problem to be solved. It may also be mentioned that a single detector coil may be used in place of the two detector coilsl and that this detector coil may be placed in the same sition as either one o! the coils shown in Hg. or that it may be placed at any position on th iron core I, or in any other position in which is linked by at least a portion o! the iiux in the magnetic circuit. v

The energizing coil 8 may be of convenient aile to produce an optimum amount ot iiux in the core I, and its dimensions will depend largely upon the requirements oi detection. the crosssection oi the core I, and the amount of economically available power. The detector coils l and I8 are preferably provided with a relatively large number oi' turns o! tine wire. so that a maximum voltage will be generated by such coils for a minimum change in reluctance o! the air path between the poles 2 and l.

Referring to Fig. 2, I have shown a somewhat modiiied arrangement which is better suited for larger conveyor belts than the arrangement shown in Fig. l. A conveyor belt is shown at Il carrying a body of material I6 having a width transverse to the direction of movement of the conveyor belt which is relatively greater than its height, and a substantially E-shaped energizing core is shown at I1 arranged with its outer legs I8 and 20 and its central leg I8 extending in a direction transverse to the of the body ot material on the conveyor belt and facing said path. The core Il is elongated between the outer legs I8 and 20 in the direction of the transverse width of the moving body o! material. Energizing coils are shown at 2|, 22 and 23 on the respective legs Il, I8 and 20 and are preferably connected to terminals 24 and 2l in such manner as to produce a magnetic iiux of one polarity in the legs I8 and 20 and a magnetic iiux of opposite polarity in the center leg I9. An elongated detector core member 28 is shown spaced from the faces oi' the legs I8, I8 and 20 and positioned so that the ux from said legs passes through an air path oi substantial dimensions which is interposed in the path of the body of material to subject the material to magnetic scrutiny, and also so that magnetic poles of the same polarity are produced in the opposite ends of the member 28. Detector coils 2l and 28 are shown wound on the detector core :org

member 28 at positions spaced from the central portion of said core member. The coils 2I and 28 are shown connected in parallel and to terminals 28 and 80 which may be associated with a suitable work circuit.

The arrangement shown in Iiig` 2 provides a somewhat more uniform distribution oi iiux through a large body of material as shown at I8, than the arrangement shown in Fig. 1. For best results the dimension B should be approximately equal to the distance between the faces oi' any one of the legs and the core member 2l.l If desired, the coils 21 and 28 may be connected in series or ,may be replaced by a single coil. It will be appreciated also that a detector coil may be placed at any position which is linked by at least a portion of the magnetic ilux which ilows in the circuit comprising the E-shaped core I l, the core member 26, and the air paths between said core members.

It may be advantageous In some instances to provide means for opposing the effect oi' voltage variations in the energizing circuit on the voltage induced in the detector coils, especially when the energizing circuit is subject to unavoidable voltage variations. In Fig. 9 an arrangement is path oi movement illustrated which may be used. by way ot example. in conjunction with the apparatus shown in Fig. 2 and for purposes of illustration the detector core oi Fig. 2 isshown provided with "buck-out" coils 21a and 20a which are connected in parallel and are adapted for parallel connection through 'terminals lla and Ila to terminals Il and 2i which are connected to the source oi energizing current. The coils 21a and lla are so proportioned and arranged as to produce iluxes which neutralize the fluxes produced in the core by the energizing coils 2l, 22, and 28. Thus voltage changes in the energizing circuit will produce no appreciable change in the iiux linking the detector coils 21 and Il, while changes in reluctance of the magnetic circuit occasioned by the presence of a foreign magnetic body will produce an unbalanced circuit condition which causes a change in Eux linkage of either one cr both of the coils 21 and 2l and the production of a potential difference between the terminals 20 and III.

In Fig. 3 I have shown an arrangement which is particularly applicable to conveyor belts which are carrying relatively thin layers of material. A conveyor belt is shown at 3| carrying a relatively thin layer of material I2, and a substantially E-shaped energizing core is shown at 33 with the legs il, 35 and thereof extending in a direction transverse to the path of movement oi' the body of material and facing said path. Coils are shown at 81, Il and 39 carried by the respective legs 34, 35 and n and connected to power supply terminals 40 and 4i in such manner as to produce a magnetic flux of one polarity in the outside legs 3l and 38 and of opposite polarity in the center leg 35. Detector coils are shown at I! and I3 wound on the respective legs 34 and I6 and connected in series and to a pair of terminals M and 45 which may be associated with a suitable work circuit. For best operation it is preferable that the level of the material above the core be located at a distance not in excess oi' about one-half the inter-pole separation represented by the dimension C. The magnetic circuit in this instance is represented by the E- shaped core 33 andthe air path between the respective core legs which is interposed in the path of the material carried by the belt 3|.

It will be appreciated that the coils 42 or 43 may be omitted and a single coil provided on the center leg 35. It will also be apprecaited that coils may be provided on each leg and may be connected either in series or in parallel.

The above showings are primarily schematic, and are not intended to represent specific proportions or size oi' the respective elements of the apparatus. The presence of a foreign magnetic body, such as a bolt, in the conveyed material is indicated at F in Figs. 1 and 2, in exaggerated scale.

In Figs. 4 through 6 I have shown a preferred embodiment of the apparatus illustrated diagrammatically in Fig. 2. A conveyor belt is shown at 5| carrying material 52 having a width transverse to the direction of movement of the conveyor belt which is relatively greater than its height, and an E-shaped energizing core is shown at 5I provided with outer legs 5l and M and a central leg 55 upon which are wound suitable coils 51. 'I'he core 5l is elongated between the outer legs 54 and 56 in the direction oi the transverse width oi the belt 5|. Since the conveyor belt BI may be of considerable width, for example,

on the order of four feet, the mass o! iron in the E-sbaped ocre Il may be considerable, and I have shown the core Il clamped between angle members Il which may be supported by a suitable foundation of concrete or the like. An elongated detector core is indicated at l0 and is shown as comprising a core Il of soft iron rods upon which are wound suitably insulated detector coils Il. A ,ie'n'gth o! iron pipe is shown at l2 between the coils Il and similar lengths ci pipe are shown at which pipes serve as a casing for the core lll. The pipe 62 serves to4 space the coils Il, and the pipes Il, which may be secured to frame members Il, serve to position the coils with respect to the energizing core Il. Fiber washers Il may be provided at the sides of the coils Il to prevent damage thereto by the respective pipe ends. Caps may be provided at I! to hold the core ill in position and to provide a more iinished appearance to the apparatus. Saddle clamps I1 are shown secured to the outside legs of the energizing core and the frame members Il are shown as secured thereto.

The frame members 6I, which are shown as iron channels. serve not only to support the core 59 but also to decrease the reluctance of the magnetic circuit lestablished between the core l) and the elongated core member I9, by decreasing the reluctance between the respective outside legs of the energizing core and the respective adjacent ends of the detector core I9. This serves to increase the total ilux between the center leg and the elongated core member. The connections to the energizing coils 51 and the detector coils i are omitted and it may be assumed that the connections are the same as shown in Fig. 2.

It will be appreciated that buck-out arrangements may be associated with the form of apparatus illustrated in Figs. 4 to 6, for example by providing buck-out coils on the core I0 arranged and energized in accordance with the showing in Fig. 9. It is also to be understood that other forms oi buck-out devices may be employed in which the buck-out current supplied to the buck-out coils on the detector core is obtained through the transformer action of coils provided on the energizing core. It is also within the contemplation of this invention to apply the buck-out eiIect directly on the potentials induced in the detector circuit as by taking a potential responsive to the changes in potential of the energizing source and applying it in opposition to the detector coil potential. In these last-mentioned forms of buck-out devices, phase relations of the various currents involved must be considered and suitable circuits employed when necessary to bring about the desired operation, as will be apparent to those skilled in the art.

A form of work circuit which may be associated with the detector coils of any oi the above forms of apparatus, as by connection to the terminals Il and I2 of Fig. 1, 29 and 30 of Fig. 2, or M and 45 of Fig. 3, is illustrated in Fig. 7, the positions of the switches and relays corresponding to normal positions prior to starting the conveyor belt. Referring to said gure, a motor 1I which may be used to operate any of the conveyor belts shown herein, for example, the conveyor belt Il in Fig. 4, is shown connected through a starting switch 12 to a three-phase power supply. One lead l2 of the power supply is shown connected through actuating coil 1I oi' a starting switch '12, thence through back contact I3 o! a relay 14 and connections 88 and 88 to another lead Il oi the power supply, through a normally open push-button 1l. Upon pressing push-button 'Il the circuit of the coil 'Il is closed. operating the starting switch 12 and maintaining coil 18 in energized relation by establishing contact through normally closed push-button 8|, contact 8l of the starting switch 12 to line connection 84, rendering the push-button 1l inoperative.

A normally open relay is shown at 18 with its terminals 11 and "adapted for connection to a pair of the above-mentioned detector coil terminals. 'I'his relay should be oi sumcient sensitivity to close its contact upon receiving a minimum voltage impulse from the associated detector coils in response to the presence of a body o! magnetic material of given minimum size. Upon receiving an impulse this relay will momentarily close, energizing the coll of relay 14 for a sumcient time to 'establish connection at its front contact 88. This relay 14 may be of a type well known to the art which will close its contact in response to a short energizing impulse and will maintain its contact closed for a given time interval after the cessation o! the impulse, returning to its position in contact with its front contact 83 at the end of the time interval. Such a relay may be dash-pot or motor operated after a manner well known to the art and need not be described in detail herein. The break oi' the circuit of relay 'i4 with its back Contact Il will break the circuit to coil 1I, opening switch 12 to stop the motor 1|. Closing of relay Il with its iront contact 86 will energize a warning horn 19 and operate the horn for the above-mentioned given time interval. Upon return of the relay 14 to a position contacting its back contact 8l, the motor 1| may be set in operation again by pushing the start button 15.

The apparatus of this invention is not limited to use with conveyor belts but may be used in conjunction With hoppers, for example, to detect the presence of magnetic material in non-magnetic materials which are being transferred from one container to another through a hopper. The apparatus may also be used for detecting dangerous Weapons or steel tools or the like carried by persons; and referring to Fig. 8, a doorway is shown at 9| through which persons suspected of carrying contraband magnetic materials are caused to pass. An energized core member l2 is positioned at one side of the doorway 8|, and a detector core member 88 carrying detector coils 94 is positioned at the other side o1' the doorway. Magnetic frame members 95 are positioned above and below the door frame and serve to connect the cores 92 and 83. This arrangement corresponds in general to the arrangement shown in Fig. 4 and may be connected to operate in the same manner.

t should be noted that in any of the forms described above the core members may be oriented in any direction With respect to the hortzontai in accordance with the conditions encounw tered as iong a substantially constant magnetic flux is produced in an air path which is interposed in the path ot the material suspected oi containing magnetic least a portionoi I claim:

l. An apparatus for subjecting a relatively large moving body of material to magnetic scrutiny, such body oi material being carried on a 25 conveyor member and having a width which is relatively greater than its height as measured transversely of the direction of movement thereoi, tor the detection o! the presence of a body oi magnetic material in such moving body of material, which comprises: a substantially E-shaped core of magnetic material having outer legs and a central leg extending toward and in a direction transverse to the path of movement of said material, said core being elongated between said outer legs in the direction of the transverse width of the moving body oi material; means for energizing the legs of said E-ahaped core t0 produce a magnetic ilux oi one polarity in the outside legs thereof and a magnetic iiux o! opposite polarity in the center leg thereof; an elongated core member spaced from said legs and positioned so that the ilux from said legs passes through an air path oi substantial dimensions interposed in the path oi! said body to produce magnetic poles oi' the same polarity in opposite ends o! said core member; detector coils wound on said elongated core member at positions spaced from the central portion thereof; and a work circuit associated with said detector coils and responsive to changes in voltage induced in said coils by changes in reluctance in said air path produced by movement of a magnetic body through said air path.

2. An apparatus as set forth in claim 1, and also comprising a frame member oi magnetic material carried by each outer leg oi said E-shaped core and serving to position said elongated core member and secured thereto adjacent an end, whereby the reluctance of the magnetic circuits established between said E-shaped core and said elongated core member is decreased between said opposite ends oi said elongated core member and said outer legs, and the iiux between said central leg and said elongated core member is increasedr HUGH E. WURZBACH. 

